The present invention relates to rotating electrical machines and, more particularly, to a stator used in rotating electrical machines having an improved stator coil end turn configuration.
Aircraft systems include various types of rotating electrical machines, such as alternating current (AC) motors and generators of various designs. Generally, an AC machine includes a rotor and a stator. If the machine is operated as a motor, electrical power is supplied to the stator to develop a rotating electrical field. This rotating electrical field generates a torque in the rotor causing it to rotate. If the machine is operated as a generator, electrical power is supplied to the rotor to generate a magnetic field. A prime mover is coupled to the rotor causing it, and thus the generated magnetic field, to rotate. This rotating magnetic field induces a voltage into the stator, which supplies electrical power to a load.
A stator for AC machines may typically include a stator core having a plurality of wire coils wound around it. The stator core is generally formed by laminating a plurality of ring plates, and includes an inner circumference having a plurality of slots that extend along its axis. In some stator designs, the wire coils are coated with an electrically insulating enamel, and are wound around the stator core by inserting a portion of each coil into, and through, two of the slots. Thus, with this design, each of the wire coils includes two slot-insertion segments that are inserted in, and pass through, separate slots in the stator core, and a non-slot-insertion segment that extends away from the end of the stator core. The non-slot-insertion segments are used to transfer electrical energy to or from the stator, depending upon the machine""s application as a motor or generator. As a result, preventing electrical interference between the individual wire coils is generally desired.
One way of preventing electrical interference between adjacent stator coils is to include a knuckle bend on the non-slot-insertion segments to provide sufficient spacing between adjacent coils. However, in some cases it has been found that the insulating enamel applied to the wire coils cracks over time because of the tight radius of the knuckle bend. With cracks in the insulating coating, electrical interference between the coils can occur. Also, when the stator exudes heat during operation, the likelihood of the enamel peeling off increases if there is a crack. Similarly, electrical interference is increased in this case as well. Moreover, the knuckle bend in some instances exceeds manufacturing tolerances, which can lead to premature failures. In addition, the length of the non-slot-insertion segments in current stator coils adds to the overall electrical resistance of the stator, which can adversely affect the overall efficiency of the electrical machine.
Therefore, there is a need for a stator that decreases the likelihood of electrical interference between stator coils, that decreases the likelihood for a mechanical failure of the stator coils, and that increases the overall efficiency of the electrical machine into which it is installed. The present invention addresses one or more of these needs.
The present invention provides a stator core that not only increases machine efficiency, but has an increased life. Additionally, the present invention decreases the likelihood of electrical interference between the coils.
In one embodiment of the present invention, and by way of example only, a stator for a rotating electrical machine includes a stator core, at least two longitudinal slots, and at least one stator coil. The stator core has an outer circumferential surface and an opening therethrough that forms an inner circumferential surface. The longitudinal slots are formed in the inner circumferential surface of the stator core. The stator coil has a first slot-insertion segment and a second slot-insertion segment interposed by a non-slot-insertion segment. The first and second slot-insertion segments extend parallel to one another in a first plane and are inserted, one each, within a separate slot. The non-slot-insertion segment has a first non-twisted segment and a second non-twisted segment interposed by a twisted segment. The twisted segment is twisted a predetermined number of degrees and includes at least a portion thereof that is bent at a predetermined angle relative to a second plane that is parallel to the first plane.
In another exemplary embodiment, a stator for a rotating electrical machine includes a stator core, at least two longitudinal slots, and at least one stator coil. The stator core has an outer circumferential surface and an opening therethrough that forms an inner circumferential surface. The longitudinal slots are formed in the inner circumferential surface of the stator core. The stator coil has a first slot-insertion segment and a second slot-insertion segment interposed by a generally V-shaped non-slot-insertion segment. The first and second slot-insertion segments extend parallel to one another in a first plane and are inserted, one each, within a separate slot. The non-slot-insertion segment has an apex formed thereon at a predetermined position, and the apex is bent at a predetermined angle relative to a second plane that is parallel to the first plane, and includes at least a portion therof that is twisted a predetermined number of degrees.
In still another exemplary embodiment, a rotating electrical machine includes a rotationally mounted rotor and a stator. The stator surrounds the rotor and includes a stator core, at least two longitudinal slots, and at least one stator coil. The stator core has an outer circumferential surface and an opening therethrough that forms an inner circumferential surface. The longitudinal slots are formed in the inner circumferential surface of the stator core. The stator coil has a first slot-insertion segment and a second slot-insertion segment interposed by a non-slot-insertion segment. The first and second slot-insertion segments extend parallel to one another in a first plane and are inserted, one each, within a separate slot. The non-slot-insertion segment has a first non-twisted segment and a second non-twisted segment interposed by a twisted segment. The twisted segment is twisted a predetermined number of degrees and includes at least a portion thereof that is bent at a predetermined angle relative to a second plane that is parallel to the first plane.
Other independent features and advantages of the preferred stator will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.